littoral \LIH-tuh-rul\ adjective/noun
: (adj) of, relating to, or on a coastal or shore region, especially a seashore
: (n) a coastal region, especially the zone between the limits of high and low tides.

Sample Usage:
"Professor Henslow tells me, he believes that nearly all the plants which I brought from these islands, are common littoral species in the East Indian archipelago". --Charles Darwin, The Voyage of the Beagle